Generally, in large systems, such as production lines or computer systems, a supervising system is provided for identifying faults in the system. A number of detectors are used, each detector providing data to a supervising unit. If data from one detector indicates a faulty unit, an alarm is issued.
Thus, alarms may be issued for minor faults as well as major faults, which means that the operator has to deal with a number of alarms, often even in situations when the system is functioning. Also, errors tend to propagate to the system, so that the same fault can give rise to a number of alarms, which can be very confusing. For example, a low supply voltage can result in bit errors on transmission links, problems in locking a phase-locked loop, distorted radio transmission, and other faults, all resulting from the same problem.